Vascular endothelial growth factor and the in vivo increase in plasma extravasation in the hamster cheek pouch

1. The purpose of this study in the hamster cheek pouch was to determine whether or not vascular endothelial growth factor (VEGF) induced changes in plasma extravasation and if so, the mechanism(s) involved. 2. The cheek pouch microcirculatory bed of the anaesthetized hamster was directly observed under microscope and the number of vascular leakage sites, as shown by fluorescein isothiocyanate (FITC-dextran, 150 kD) extravasation, was counted. Drugs and VEGF were applied topically. VEGF from 0.05 to 0.5 microg ml(-1) (1.2 to 12 nM) produced a dose-dependent increase in the number of microvascular leakage sites from virtually none in basal conditions to up to 250 in some pouches. The effects of VEGF (0.1 microg ml(-1) or 2.4 nM) were blocked in a concentration-dependent manner by the non-specific heparin growth factor antagonist TBC-1635 (0.1, 1 and 3microM). The placenta growth factor (PlGF-1: 0.1 and 0.5 microg ml(-1) or 3.4 and 17 nM) did not increase plasma extravasation, per se, but abolished the effects of VEGF (2.4 nM). 3. The increases in microvascular leakage produced by VEGF (2.4 nM) were partially but significantly (P<0.05) inhibited by genistein (5 and 10 microM, up to 33% inhibition), LY 294002 (30 microM, 41%), bisindolylmaleimide (1 microM, 65%) and virtually abolished by indomethacin (3 microM, 88%) and L-nitro-arginine (10 microM, 95%), these drugs being inhibitors of tyrosine kinase, phosphatidylinositol-3-kinase, protein kinase C, cyclo-oxygenase and nitric oxide synthase respectively. None of these inhibitors, at the concentration tested, induced alone an increase in plasma extravasation. 4. These results indicate that the VEGF-induced plasma extravasation may involve the stimulation of VEGF-R2 (Flk-1/KDR) and the activation of phosphatidylinositol-3-kinase and protein kinase C. The production of both nitric oxide and prostaglandin is required to observe an increase in vascular leakage.